Photochemical reactions of organic molecules on semiconductor surfaces are of interest as a means of synthesizing patterned structures with specific chemical functionalities. The adsorption of 4-chloro- and 4-iodoaniline on the GaN(0001)-(1x1) surface, and the effects of subsequent exposure to near-UV or vacuum-UV radiation, have been studied using primarily UV photoemission and electron energy loss spectroscopies, supported by ab initio quantum-chemical modeling. Both 4-haloanilines adsorb via the molecular NH@sub 2@ group, with the phenyl ring intact, as does aniline itself.@footnote 1@ Like aniline, both are very reactive with the clean GaN(0001)-(1x1) surface, requiring only a small dose to achieve saturation coverage (ca. 0.29 molecules/surface site). 4-Iodoaniline is photochemically active as an adsorbate on GaN, as expected from its apparent behavior in non-polar solvents. UV radiation promotes dissociation of the molecular C-I bond, leading to the transfer of I to available sites on the GaN surface. The molecular C-I bond is intact prior to irradiation, as suggested by the changes in ELS and UPS data seen to result from UV exposure. The photochemical activity of 4-chloroaniline adsorbed on GaN is at present uncertain, but it appears to be relatively inert, again consistent with its behavior in non-polar solvents. Similar results were obtained for both n- and p-type GaN, suggesting that the photochemistry is not mediated by excited carriers from the GaN substrate.
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@footnote 1@ V.M. Bermudez, Surf. Sci. 499 (2002) 109, 124.